U.S. patent number 6,431,555 [Application Number 09/805,359] was granted by the patent office on 2002-08-13 for leaf seal for inner and outer casings of a turbine.
This patent grant is currently assigned to General Electric Company. Invention is credited to David Leach, Mark Stewart Schroder.
United States Patent |
6,431,555 |
Schroder , et al. |
August 13, 2002 |
Leaf seal for inner and outer casings of a turbine
Abstract
A plurality of arcuate, circumferentially extending leaf seal
segments form an annular seal spanning between annular sealing
surfaces of inner and outer casings of a turbine. The ends of the
adjoining seal segments have circumferential gaps to enable
circumferential expansion and contraction of the segments. The end
of a first segment includes a tab projecting into a recess of a
second end of a second segment. Edges of the tab seal against the
sealing surfaces of the inner and outer casings have a narrow
clearance with opposed edges of the recess. An overlying cover
plate spans the joint. Leakage flow is maintained at a minimum
because of the reduced gap between the radially spaced edges of the
tab and recess, while the seal segments retain the capacity to
expand and contract circumferentially.
Inventors: |
Schroder; Mark Stewart
(Hendersonville, NC), Leach; David (Simpsonville, SC) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
25191358 |
Appl.
No.: |
09/805,359 |
Filed: |
March 14, 2001 |
Current U.S.
Class: |
277/628; 277/630;
277/632; 415/230 |
Current CPC
Class: |
F01D
11/005 (20130101); F16J 15/0887 (20130101); F05D
2240/55 (20130101); F05D 2230/642 (20130101) |
Current International
Class: |
F01D
11/00 (20060101); F16J 15/08 (20060101); F16J
015/02 (); F01D 025/00 () |
Field of
Search: |
;415/230,231
;277/632,630,628 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Knight; Anthony
Assistant Examiner: Peavey; Enoch E
Attorney, Agent or Firm: Nixon & Vanderhye
Government Interests
This invention was made with Government support under Contract No.
DE-FC21-95MC31176 awarded by the Department of Energy. The
Government has certain rights in this invention.
Claims
What is claimed is:
1. In a turbine having radially spaced inner and outer casings and
generally annular sealing surfaces, a seal for sealing across the
sealing surfaces and between high and low pressure regions on
opposite sides of the seal, said seal comprising: first and second
seal segments disposed in a generally common plane in end-to-end
relation to one another, a first end of said first segment having a
projection and a second end of said second segment in opposition to
said first end having a recess for receiving the projection, said
first and second ends having edges defining circumferentially
extending gaps therebetween; said projection having radially spaced
edges for sealingly engaging the respective sealing surfaces of the
inner and outer casings; and radially spaced edges of said recess
in opposition to respective edges of said projection defining
radial gaps therebetween each having a smaller gap width than the
width of each of the circumferential gaps between said first and
second ends.
2. A seal according to claim 1 including a cover plate overlying
said first and second ends and said gaps to minimize flow between
the high and low pressure regions across said seal.
3. A seal according to claim 2 wherein said cover is secured to one
of said first and second seal segments and spans the gaps between
the segments to overlie a portion of another of said first and
second seal segments.
4. A seal according to claim 1 including a seal carrier carried by
one of the inner and outer casings for supporting said seal and a
spring carried by said carrier for biasing at least one seal
segment into sealing engagement with the sealing surfaces.
5. A seal according to claim 1 wherein the circumferential gaps are
substantially uniform throughout their radial extent.
6. A seal according to claim 1 wherein the circumferential gaps
have a circumferential extent sufficient to enable expansion and
contraction of said segments circumferentially toward and away from
one another, respectively.
7. A seal according to claim 1 including a cover plate overlying
said first and second ends and said gaps to minimize flow between
the high and low pressure regions across said seal, said cover
plate being secured to one of said first and second seal segments
and spanning the gaps between the segments to overlie a portion of
another of said first and second seal segments.
8. A seal according to claim 1 wherein said cover plate is secured
to one of said first and second seal segments and spans the
circumferential gaps between the segments to overlie a portion of
another of said first and second seal segments, a seal carrier
carried by one of said inner and outer casings for supporting said
seal and a spring carried by said carrier for biasing at least one
seal segment into sealing engagement with the sealing surfaces.
9. In a turbine having radially spaced inner and outer casings and
generally annular sealing surfaces, an annular seal for sealing
across the sealing surfaces and between high and low pressure
regions on opposite sides of the seal, said seal comprising: first
and second elongated arcuate seal segments disposed in a generally
common plane in spaced circumferential end-to-end relation to one
another, a first end of said first segment having a
circumferentially extending tab and a second end of said second
segment in opposition to said first end having a circumferentially
opening recess for receiving the tab, said first and second ends
defining circumferentially extending gaps therebetween; said tab
having radially spaced, circumferentially-extending edges for
sealingly engaging the respective sealing surfaces of the inner and
outer casings; radially spaced edges of said recess in opposition
to said radially spaced edges of said tab defining radially
extending gaps therebetween each having a smaller gap width than
the width of each of the circumferential gaps between said first
and second ends; and a cover plate overlying said first and second
ends and said gaps to minimize flow between the high and low
pressure regions across said seal.
10. A seal according to claim 9 wherein said cover plate is secured
to one of said first and second seal segments and spans the
circumferential gaps between the segments to overlie in sliding
relation a portion of another of said first and second seal
segments.
11. A seal according to claim 9 including a seal carrier carried by
one of said inner and outer casings for supporting said seal and a
spring carried by said carrier for biasing at least one seal
segment into sealing engagement with the sealing surfaces.
12. A seal according to claim 9 wherein the circumferential gaps
are substantially uniform in width throughout the radial extents of
the gaps.
13. A seal according to claim 9 wherein the circumferential gaps
have a circumferential extent sufficient to enable expansion and
contraction of said segments circumferentially toward and away from
one another, respectively, during operation of the turbine.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a seal between sealing surfaces on
inner and outer turbine casings for sealing between high and low
pressure regions on opposite sides of the seal and particularly
relates to arcuate leaf seal segments having a tab-and-groove
arrangement along adjoining ends cooperable with the sealing
surfaces for minimizing leakage flow through the seal.
In an advanced gas turbine design, an annular inner casing is
mounted for radial and axial expansion and contraction relative to
a surrounding annular outer casing. Each casing comprises a pair of
generally semi-circular casing halves joined at their midline to
one another. The inner casing mounts the first and second-stage
nozzles and shrouds for the turbine, as well as ancillary parts
for, among other things, carrying cooling circuits for the nozzles
and shrouds. The outer casing is stationary and mounts the
combustors and ancillary parts including for supplying the cooling
medium to the inner casing, the shrouds and nozzle stages.
Compressor discharge air at high pressure is supplied in a region
forwardly of the inner casing and a portion of the outer casing for
flow to the turbine combustors. A lower pressure region lies
between the inner and outer casings and which region extends aft
from an axial location along the turbine corresponding generally to
the first bucket. It has been the practice to provide an annular
seal between adjacent annular sealing surfaces on the inner and
outer casings to seal between these high and low pressure
regions.
Because of the relative radial and axial expansion of the inner and
outer casings, it has been customary to provide a series of arcuate
leaf seals carried by the inner casing in arcuate end-to-end
relation relative to one another and overlying radially spaced,
axially forwardly facing sealing surfaces of the inner and outer
casings. This end-to-end sealing arrangement provides
circumferentially extending gaps between end edges of each pair of
adjacent leaf seals necessary to accommodate expansion and
contraction of the casings and preclude arch binding of the seals.
To minimize the flow through each gap, a cover plate overlies
adjoining ends of the leaf seals along a surface of the seals
opposite from the sealing surfaces of the inner and outer casings.
While these leaf seals with cover plates have reduced the flow from
the high to the low pressure regions, significant leakage remains.
For example, with the seals engaging the radially spaced
circumferentially extending sealing surfaces of the inner and outer
casings and the cover plate overlying the gaps between adjoining
ends of the seal plates, high pressure flow occurs between the
overlying cover plate and the circumferential gap between
registering end edges of the seal plates. Accordingly, there is a
need to provide a seal which will further minimize flow between the
high and low pressure regions on opposite sides of the seal
plates.
BRIEF SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention,
there is provided arcuately segmented seal plates for sealing
against radially spaced, axially facing sealing surfaces of the
inner and outer casings for eliminating or minimizing the leakage
flow between high and low pressure regions on opposite sides of the
seal. Particularly, the seal includes a plurality of arcuate
segmented seal plates disposed in an annular array thereof about
the rotor axis between the high and low pressure regions. The seal
plates are preferably carried by the inner casing and have
sufficient radial extent to seal against the annular sealing
surfaces of both the inner and outer casings. At the registering
adjacent end edges of the seal plates, there is provided a
projecting tab on a first end of a first seal plate and a recess on
a second end of the registering seal plate for receiving the tab.
The tab has circumferentially extending, radially spaced sealing
portions or edges which seal against the respective arcuate sealing
surfaces of the inner and outer casings. The end edge of the tab,
as well as the end edges straddling the tab at the first end of the
first seal plate, are respectively spaced circumferentially from
the edge at the base of the recess and the end edges straddling the
recess at the second end of the second seal plate to provide
circumferential gaps therebetween. These circumferentially offset
and circumferentially extending gaps enable the seal plates to
expand and contract in circumferential directions relative to one
another without engaging or binding up one another.
To minimize or eliminate the leakage flow past this circumferential
gap between adjacent arcuate seal plates, a cover plate overlies
the first and second ends of the respective plates. The cover plate
is secured, for example, by welding to one of the seal plates and
overlies the adjacent seal plate spanning the gap between the
plates. The reduced leakage flow is created by reducing the size of
the flow path, together with a flow turn. That is, with the
radially spaced edges of the tab engaging the sealing surfaces of
the inner and outer casings, a reduced clearance between those
edges and the radially spaced edges of the recess significantly
reduces the leakage flow through the juncture of the seal plates
between the high and low pressure regions. Concurrently, the
circumferential gap between adjacent seal plates remains the same
as in the prior seals, enabling the leaf seal plates to
circumferentially expand and contract relative to one another.
In a preferred embodiment according to the present invention, there
is provided in a turbine having radially spaced inner and outer
casings and generally annular sealing surfaces, a seal for sealing
across the sealing surfaces and between high and low pressure
regions on opposite sides of the seal, the seal comprising first
and second seal segments disposed in a generally common plane in
end-to-end relation to one another, a first end of the first
segment having a projection and a second end of the second segment
in opposition to the first end having a recess for receiving the
projection, the first and second ends having edges defining
circumferentially extending gaps therebetween, the projection
having radially spaced edges for sealingly engaging the respective
sealing surfaces of the inner and outer casings and radially spaced
edges of the recess in opposition to respective edges of the
projection defining radial gaps therebetween each having a smaller
gap width than the width of each of the circumferential gaps
between the first and second ends.
In a further preferred embodiment according to the present
invention, there is provided in a turbine having radially spaced
inner and outer casings and generally annular sealing surfaces, an
annular seal for sealing across the sealing surfaces and between
high and low pressure regions on opposite sides of the seal, the
seal comprising first and second elongated arcuate seal segments
disposed in a generally common plane in spaced circumferential
end-to-end relation to one another, a first end of the first
segment having a circumferentially extending tab and a second end
of the second segment in opposition to the first end having a
circumferentially opening recess for receiving the tab, the first
and second ends defining circumferentially extending gaps
therebetween, the tab having radially spaced,
circumferentially-extending edges for sealingly engaging the
respective sealing surfaces of the inner and outer casings,
radially spaced edges of the recess in opposition to the radially
spaced edges of the tab defining radially extending gaps
therebetween each having a smaller gap width than the width of each
of the circumferential gaps between the first and second ends and a
cover plate overlying the first and second ends and the gaps to
minimize flow between the high and low pressure regions across the
seal.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary off-axis radial cross-sectional view of a
portion of the first stage of a gas turbine illustrating inner and
outer casings thereof and a leaf seal therebetween;
FIG. 2 is an enlarged axial cross-sectional view of the seal of
FIG. 1 taken about on line 2--2 in FIG. 4;
FIG. 3 is a fragmentary axial view of the seal looking from left to
right in FIG. 1; and
FIG. 4 is an enlarged cross-sectional view illustrating the sealing
surfaces of the seal plate tab and the sealing surfaces of the
inner and outer casings taken generally about on line 4--4 in FIG.
2.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings, particularly to FIG. 1, there is
illustrated a portion of a gas turbine including an inner shell or
casing 10, an outer shell or casing 12 and a seal 14 constructed in
accordance with the present invention sealing between axially
forwardly facing sealing surfaces along the inner casing 10 and
outer casing 12. It will be appreciated that both the inner and
outer casings 10 and 12, respectively, are annular in shape about
the axis of the turbine rotor with each being formed in two
semi-circular halves joined at a midline. The inner casing 10 is
joined to the outer casing 12 by a plurality of pins, not shown,
arranged about the axis and which may be of the type described and
illustrated in U.S. Pat. No. 6,079,943, of common assignee
herewith, the disclosure of which is incorporated herein by
reference. The inner shell 10 carries the first and second stage
nozzles 16 and 18 and shrouds 20 about the first and second-stage
buckets, one shroud being illustrated surrounding a first-stage
bucket 22. The stages, of course, receive the hot gases of
combustion from a combustor which, in turn, is supplied with high
pressure compressor discharge air from a high pressure region 24
forwardly of the seal 14. Between the inner and outer casings 10
and 12, respectively, is a low pressure region 26. The seal 14
hereof seals between the high and low pressure regions 24 and 26,
respectively, with minimized leakage flow between the regions.
Referring now to FIG. 4, the inner and outer casings have contact
or sealing surfaces 30 and 32, respectively, which are annular
about the rotor axis. The seal 14 spans in a radial direction
between the inner and outer casings in sealing contact with the
sealing surfaces 30 and 32. Because the inner casing 10 expands and
contracts in radial and axial directions relative to the outer
casing 12, the seal 14 between the casings is comprised of a
plurality of arcuate leaf seal plates or segments 34 (FIGS. 2 and
3) disposed in end-to-end relation to one another about the rotor
axis. Each seal segment 34 is supported along an arcuate inner
portion thereof by the inner shell 10 and a leaf seal segment
carrier 36 (FIG. 4) secured to the inner shell. The carrier 36 is
fixed to the inner shell, preferably by bolts, and includes a
plurality of pins 38 at circumferentially spaced positions along
the carrier which are disposed in circumferential slots along the
inner edge portion of the seal plates 34 (FIG. 3). A leaf spring 40
extends about each pin 38 and includes a radial outward directed
blade bearing against the forward axial surface of a seal plate 34.
At least two or more springs 40 are provided each seal plate for
initially maintaining each seal plate 34 in engagement with the
sealing surfaces 30 and 32.
To accommodate the circumferential expansion and contraction of the
seal plates 34 relative to one another, the end edges 44 (FIG. 2)
of adjoining seal plates are spaced one from another, forming a
radially extending gap 46. If, as in conventional leaf seal
construction, the gap extends linearly and radially between the
circumferentially opposed end edges of the leaf seals, the portion
of the circumferential gap 46 between the seal surfaces 30 and 32,
even with a cover plate spanning the joint between the ends of the
adjacent seal plates, would provide a significant leakage path
between the high and low pressure regions 24 and 26,
respectively.
In accordance with a preferred embodiment of the present invention,
the leakage path through the circumferential gap between adjacent
ends of the seal plates is minimized by changing the configuration
of the seal at the juncture of adjacent seal plates. With reference
to FIG. 2, a first seal segment, e.g., plate 50, of the plurality
of seal plates 34 is provided with a projection, e.g., an end tab
52, adjacent a first end 51 thereof. The end tab 52 has inner and
outer radially spaced, circumferentially extending edges 54 and 56,
respectively. The second end 58 of a second seal segment, e.g.,
plate 60, of the plurality of seal plates 34 has a generally
corresponding recess 62 for receiving the tab 52. The recess 62 is
bounded by inner and outer radially spaced, circumferentially
extending edges 64 and 66, respectively, and a radially extending
edge 68 along the base of the recess in circumferential opposition
to a radially extending edge 70 at the end of tab 52. The edges 44
and 70 of the first seal plate 50 and the edges 72 and 68 of the
second end 58 of the second seal plate 60 respectively define equal
circumferentially extending and offset gaps 46 and 74,
respectively. Additionally, the radial inner edges 54 and 64 of tab
52 and recess 62, respectively, form an inner gap 80 therebetween.
Similarly, the radial outer edges 56 and 66 of tab 52 and recess
62, respectively, form an outer gap 82 therebetween. Gaps 80 and 82
are radially spaced from one another. The gap 74 between end edges
70 of tab 52 and end edge 68 of recess 62 lies generally parallel
to gap 46. In addition, a cover plate 84 (FIG. 3) overlies the
joint between each adjoining end of the seal plates 50 and 60 on
the axial forward side of the segments 34. The cover plate 84 is
secured, preferably welded, to one or the other of the end of a
segment and is in overlying sliding relation to the other
segment.
In accordance with the present invention, the radial inner and
outer gaps 80 and 82 are provided with minimum clearances between
the edges 54, 56 of the tab and edges 64, 66 of the recess forming
the gaps 82 and 80, respectively. Those clearances are considerably
tighter than the clearances defining gaps 46 and 74. Thus, the
width of the radial gaps 80, 82 is less than the width of the
circumferential gaps 46, 74. This results from only having to
accommodate the thermal expansion/contraction of small components
52 and 62, respectively. Gaps 46 and 74 accommodate the thermal
expansion of inner shell 10 having a much greater dimension than
that of tab 52 and recess 62. Additionally, the edges 54 and 56 are
designed to maintain sealing contact with the sealing surfaces 30
and 32, respectively, throughout the full operating range of the
turbine. With the cover plate 84 applied over the adjoining ends of
the segments 34, the leakage path from the high pressure region to
the low pressure region at each joint includes the
circumferentially spaced gaps 46, the radial inner and outer gaps
80 and 82 and the circumferential gap 74 between the end edge 70 of
the tab 52 and the edge 68 of recess 62. However, because the
radial inner and outer gaps 80 and 82, respectively, are
dimensioned for a very narrow clearance therebetween and because
the edges 54 and 56 are maintained in sealing contact with the
sealing surfaces 30 and 32 of the inner and outer casings, only a
very narrow passage along those radial inner and outer gaps remains
available for flow of leakage air. Further, the leakage path
includes a 90.degree. turn from the circumferential gap 46 into the
circumferentially extending radial inner and outer gaps 80 and 82.
Thus, the majority of any leakage flow cannot pass directly axially
through the seal but first must pass radially, circumferentially
and then axially. The radially spaced gaps 80, 82 are very narrow,
have tight clearances, and minimize the leakage flow, while at the
same time, the gaps 46, 74 permit radial expansion of the seal
plate segments 34 relative to one another to prevent arch
binding.
It will also be appreciated that at steady state operation, the
high pressure region on the axial forward faces of the leaf seals
maintains the leaf seals in engagement with the sealing surfaces 30
and 32 of the inner and outer casings. Consequently, the springs 40
serve only to maintain the leaf seal plates initially biased
against the sealing surfaces 30 and 32, the contact between the
sealing surfaces 30, 32 and the leaf seal plates being maintained
at steady-state operation by the differential pressure across the
seal. Thus, the springs 40 are substantially functionally redundant
during steady-state operation.
While the invention has been described in connection with what is
presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *